This invention is drawn to hydrogel wound dressings that are inherently antimicrobial. More particularly, this invention is drawn to inherently antimicrobial hydrogels containing wound dressings wherein the hydrogel is formed by the polymerization of acrylated quaternary ammonium monomers in an aqueous media.
In the past, wounds have been treated with antimicrobial active agents applied to the wound and covered with a covering that inhibits the healing process. For example, it was conventional practice early in the 20th Century to apply an antiseptic mercury agent such as thimerosal (Merthiolate) or merbromin (Mercurochrome) and the like to a wound and then cover or wrap the wound with a bandage such as gauze or an adhesive strip having a central absorbent gauze portion.
A disadvantage of this approach is that the wound often weeps or exudes fluids such as blood, pustulation and the like. While the gauze may absorb some of these fluids, the gauze often adheres to the wound such that removal of the dressing reopens the wound.
Advances in the art have been made in both bandages and antimicrobial agents. Certain bandages now contain a nonadhering polymeric coating over or, in place of, the gauze that inhibits the adhering of the absorbent material to the wound but also inhibits the absorption of the exudate that is necessary to properly heal the wound.
Certain wound dressing materials have been used to absorb exudate and promote healing. For example, Mason, et al., U.S. Pat. No. 4,393,048 teaches a hydrogel composition which, when applied as a powder, absorbs wound exudate. The hydrogel formation may not be complete and lumps of partially hydrated powders form which, when removed, may reopen the wound.
It is known that wounds heal more rapidly and completely if kept in a slightly moist or hydrated state. Polyethylene glycol containing hydrogel wound coverings are disclosed in Spence, U.S. Pat. No. 4,226,232. These hydrogels cannot be sterilized by irradiation due to the formation of free radicals.
Rawlings et al., U.S. Pat. No. 4,657,006, illustrate wound dressings comprised of a hydrophilic polymer having moisture and vapor permeability properties. However, the exudate absorbed by the hydrophilic polymer tends to harden or solidify the polymer.
An ideal wound dressing should not only absorb exudate but also possess antimicrobial properties. For example, Matson, U.S. Pat. No. 4,728,323 discloses a wound dressing comprising a substrate coated with an antimicrobial coating of a silver salt that allegedly keeps the wound moist.
Korol, U.S. Pat. No. 4,563,184, discloses wound dressings comprising a polymer, such as poly(2-hydroxyethylmethacrylate), a solvent, such as polyethylene glycol, and a plasticizer such as DMSO. An antimicrobial agent, such as silver sulfadiazine, may be incorporated into the polymeric material.
Widra, U.S. Pat. No. 4,570,629, is drawn to absorbent hydrogel membrane wound dressings made up of hydrophilic biopolymeric copolyelectrolytes comprising a water-soluble linear anionic protein polyelectrolyte component derived from keratin and a water-soluble linear cationic biopolymer polyelectrolyte component derived from either collagen or a glucosamineglycan. The membranes may also contain antibiotics.
Klemm et al., U.S. Pat. No. 4,191,743, teache the administration of antibiotics to wounds using a wound dressing comprising at least two layers of synthetic resin arranged one above the other having an intermediate layer composed of a synthetic resin granulate having an antibiotic incorporated therein.
It is known that certain quaternary amine salts possess antimicrobial properties. Examples include benzethonium chloride and benzalkonium chloride (Bactine(copyright)). It is also known that certain quaternary amines can be incorporated into polymeric substrates to provide a certain degree of antimicrobial activity.
Rebaum et al., U.S. Pat. No. 3,898,188, teach cationic polyelectrolytes homopolymers formed from an alkyl amine halide monomer that are useful for various medical applications. These polymers are formed by the head-to-tail quaternization reaction of the monomer to form linear chains. Such polyelectrolyte homopolymers are taught to possess bacteriocidal activity and can be topically applied to traumatic skin areas such as in the treatment of burns, abrasions or cuts. However, the homopolymers do not possess gel forming capabilities and, in order to form a moisture retaining structure, must be combined with a polyvinyl alcohol or polyvinyl pyrrolidone polymer. Such combinations result in films that can impregnate gauze materials to form an antiseptic or germicidal dressing material. The homopolymers may also be converted to branch polymers having a comb-like structure by attaching the quaternary homopolymer to the backbone of a polymeric substrate such as a poly-dialkylaminoalkylacrylates or a polyalkylaminoacrylamides. Such comb-like polymers are useful for coating onto substrates such as photocopy paper. Further, the polyelectrolyte monomers can be copolymerized with anionic polymers such as polystyrene sulfonates, polyacrylates or heparin to provide copolymers that can coat surfaces such as tubes, catheters, valves and the like with a non-thrombogenic coating.
Hou et al., U.S. Pat. No. 4,791,063, teach polyionene-transformed modified polymer-polysaccharide separation matrices for use in removing contaminants of microorganism origin from biological liquids. This patent teaches that absorption of bacterial cells by ion-exchange resins is attributable to electrostatic attraction between quaternary ammonium groups on the resin surface and carboxyl groups on the bacteria cell surface.
Hansen et al., U.S. Pat. No. 5,498,478 is directed to the use of a polyethylene glycol or similar polymer as a binder material for fibers of any variety. The binder and fibers may be pretreated by slurrying the fibers in baths containing antimicrobial agents as part of the solution, thereby causing the fibers and the subsequently formed matrix of polymer and fibers to have an antimicrobial ability.
Mixon et al., U.S. Pat. No. 5,069,907 is directed to the formation and use of a polymeric sheet which may include an antimicrobial agent. This patent teaches of the inclusion of antimicrobial agents into either a pressure-sensitive layer, such as an adhesive, or in a drape used to cover a wound or other sensitive area.
Dietz et al., U.S. Pat. Nos. 5,674,561 and 5,670,557 are directed to polymerized microemulsion pressure sensitive adhesive compositions that may optionally contain antimicrobial and/or other biologically active agents. The potential antimicrobial activity of quaternary amine and quaternary ammonium salts is taught. It is further taught that an antimicrobial agent can be added so as to be contained in a specific layer of a pressure sensitive adhesive device for use as a medical skin covering and/or as a wound dressing.
Young et al., U.S. Pat. No. 5,432,000, teach the use of a polymeric network for adhering particulate materials to a fiber or fibrous product. Specifically, this patent teaches of the use of polymers, such as polyethylene glycol or polyethylene to cause the binding of particulate materials to a fiber, such as cloth. One such particulate member which could be adhered to cloth is an antimicrobial agent, such as epoxide phenol or another antimicrobial substance.
There is a need for a wound dressing that incorporates the desired properties of exudate absorption, moisture retention to the wound and antimicrobial properties into a single hydrogel structure. Such has not been previously demonstrated in the prior art.
It is therefore an object of the present invention to provide a cationic quaternary amine polyacrylate hydrogel wound dressing that is inherently antimicrobial.
Another object of this invention is to provide a hydrogel wound dressing that absorbs wound exudate and allows the wound to remain in a hydrated or moist occlusive condition.
A still further object of the invention is to provide a hydrogel formed from the polymerization of cationic quaternary amine acrylic acid ester or amide monomers wherein the formed polymers are inherently antimicrobial and, when hydrated, provide hydrogel dressings having an adhesive quality that loosely adheres to the wound to keep the wound hydrated, absorb exudate and yet is readily removed without aggravating the wound healing process.
Another object of the invention is to provide a method for treating wounds by applying to the wound an inherently antimicrobial cationic quaternary amine containing polyacrylate hydrogel to promote heating, absorb exudate and retain the wound in a moist or hydrated condition.
These and other objects are accomplished by means of an aqueous hydrogel composition comprising between about 15 to 95% by weight of a cationic quaternary ammonium polyacrylate polymer of following Formula I: 
wherein n is an integer of 2 to 3; Rxe2x80x2, Rxe2x80x3 and Rxe2x80x2xe2x80x3 are independently selected from the group consisting of H, C1 to C16 alkyl, aryl, arylamine, alkylamine, alkaryl and aralkyl; X is selected from the group consisting of O and NH; Yxe2x88x92 is an acceptable anionic counterion to the N+ of the quaternary amine and m is an integer greater than 50,000.
Alkyl groups are preferably lower alkyl, of C1 to C8 with methyl or ethyl groups being particularly preferred. Aryl is preferably phenyl but can be any suitable aromatic moiety such as those selected from the group consisting of phenyl, thiophenyl, naphthyl, biphenyl, pyridyl, pyrimidinyl, pyrazyl, pyridazinyl, furyl, thienyl, pyrryl, quinolinyl and bipyridyl and the like. Representative of an aralkyl grouping is benzyl and representative of an alkaryl grouping is tolyl. X is preferably O or NH. Representative of counterions represented by Yxe2x88x92 are members selected from the group consisting of Clxe2x88x92, Brxe2x88x92, HSO45xe2x88x92, and CH3SO4xe2x88x92 with Clxe2x88x92 being particularly preferred. Alkyl groups can be straight or branched chained and alkyl and aryl groups can be substituted by non-interfering substituents that do not obstruct with the functionality of the polymers.
The cationic quaternary ammonium polymer can be prepared in an aqueous medium and form an hydrogel in situ or can be prepared in an aqueous medium, dried and converted into a powder which can then be reconstituted in aqueous media as a hydrogel.
The polymer is prepared by the polymerization of an acrylic acid monomer according to following Formula II: 
where n, Rxe2x80x2, Rxe2x80x3 and Rxe2x80x2xe2x80x3, X, Yxe2x88x92 have the meanings given above in Formula I. Polymerization is brought about by methods known in the art such as free radical curing with an initiator induced polymerization in the presence of water by ultra-violet curing and a multi-functional cross-linking agent or by anionic 1,2 alkoxy anion induced polymerization.
The cationic quaternary ammonium polymers of this invention possess inherent microbiocidal properties and are absorbent and non-irritating to the skin or open wounds. The absorbency of the hydrogel means that, when applied as a wound dressing, fewer dressing changes are necessary, the wound heals faster and a moist healing environment is maintained. The polymers are radiation tolerant and can be sterilized by such means. Because the polymers are inherently microbiocidal, the wound is retained in a sterile environment to promote healing. Further, because the polymers are polycationic, it is possible that healing is accelerated because blood clotting is promoted due to the cationic polymer neutralizing polyanionic clotting inhibitors such as the naturally occurring anionic polysaccharide heparin.
The hydrogels are preferably prepared with a physical support structure to better retain the hydrogel over a wound. This physical support structure may be in the form an occlusive device having an impermeable backing, i.e. a patch. Since hydrogel is both inherently adhesive as well as antimicrobial, the use of more permanent adhesives may or may not be beneficial. The hydrogel can also be formed around a web or fibril support and fashioned by cutting into suitable sizes in both surface area and depth, i.e. sheets, strips, squares, circles, ovals, etc.